Rivers of air in the sky are melting huge patches of Antarctic sea ice

Rivers of warm air transported across the atmosphere have been found to play a major role in the creation of vast openings in Antarctic sea ice.

Storms are known to help trigger the openings, known as polynyas, which in the past have expanded to tens of thousands or even hundreds of thousands of square kilometres. But despite the world’s most powerful storms being a regular fixture in the Southern Ocean around Antarctica, they don’t on their own explain why the polynyas form at some times and not at others.

Now, Diana Francis at Khalifa University in Abu Dhabi, United Arab Emirates, and her colleagues think they have the answer. Combing satellite records and climate data, they looked at major polynya events in the Weddell Sea on the Antarctic coast in 1973 and 2017.

They found that flows of heat and water vapour in the sky, known as atmospheric rivers, travelled huge distances, in one case moving from the south-eastern coast of South America down to the Weddell Sea in 2017. During September that year, one river increased air temperatures in the Weddell Sea by 10°C.

It isn’t just that the rivers of heat start melting the ice pack, making it fragile and easily broken up by cyclones. “The atmospheric rivers also make the storms more intense because they provide more water vapour. They are linked, not independent,” says Francis.

The polynyas can bring benefits, such as providing nutrients to marine life. However, like melting Arctic sea ice, they matter globally because they can speed up climate change when dark open water reflects less of the sun’s energy back to space than white ice. In turn, climate change will influence future polynyas. Global warming is expected to increase the frequency of atmospheric river events by around 50 per cent if carbon emissions stay high.